The present invention relates to a semiconductor device and a production method thereof. The present invention particularly relates to an effective technology for forming, in a substrate in which a semiconductor layer is deposited on an insulating layer, an element in which a pin photodiode that converts light into a photocurrent and a MOS transistor through which the photocurrent is output are integrated. An exemplary substrate is an SOI substrate in which a silicon layer is deposited on an insulating layer.
In semiconductor photodetectors that convert light into a photocurrent, commonly known as photodiodes, there is a problem in that an optical signal available for the photodiode has a low response frequency and is hard to detect.
In order to solve this problem, a pin photodiode in which the width of a depletion layer is enlarged by placing an i region (semiconductor layer) having a suitable thickness in a pn junction and by applying reverse bias has been proposed. The pin photodiode is composed of a conductive layer having a three-layer structure in which a p region is deposited on an i region which is deposited on an n region. When the i region receives light while a voltage is applied to the p region of the pin photodiode, the i region generates electron-hole pairs in response to the light intensity. The hole is transferred to the p region and the electron is transferred to the n region under the influence of the electric field of the depletion layer, so that a current is generated in the pin photodiode in the layered direction.
The proposed pin photodiode provides high photosensitivity and can be used at high frequencies, and providing the i region allows a reduction in dark current and noise to be achieved.
A semiconductor element in which the pin photodiode is integrated with a MOS transistor, through which a photocurrent is output, to efficiently output the photocurrent generated in the pin photodiode also has been proposed.
Since the pin photodiode is composed of the conductive layer having the three-layer structure in which the p region is deposited on the i region which is deposited on the n region, the perpendicular thickness of the conductive layer is at least 2 xcexcm, and therefore, forming the pin photodiode in a substrate in which a thin semiconductor layer is deposited on an insulating layer is difficult. An exemplary substrate that may be used is an SOI substrate in which a thin silicon layer is deposited on an insulating layer.
Since an element in which a pin photodiode and a MOS transistor are integrated is directly formed in a so-called bulk silicon substrate, high-energy incident light penetrates deep into the silicon layer to generate electron-hole pairs. When the charge enters an adjacent gate, however, an accurate relationship between the incident light and an electrical signal is not realized.
Accordingly, the present invention provides a semiconductor device in which a pin photodiode and a MOS transistor are integrated on a SOI substrate and the like. The present invention has a high sensitivity and excellent electrical power saving. A production method and an electronic device are also provided.
The semiconductor device of the present invention includes an element in which a pin photodiode converts light into a photocurrent in response to a light intensity and a MOS transistor through which the photocurrent is output are integrated. The element is formed in a substrate including an insulating layer and a semiconductor layer. The semiconductor layer is deposited on the insulating layer. The pin photodiode has a p region, an i region, and an n region which are horizontally arranged in the semiconductor layer.
In the above semiconductor device, since the element in which the pin photodiode and the MOS transistor are integrated is formed in the substrate in which the semiconductor layer is deposited on the insulating layer, a substantial amount of junction leakage current flowing between electrodes is reduced. Furthermore, the high-energy incident light is transmitted through the semiconductor layer to generate electron-hole pairs in the insulating layer, and therefore, a charge entering a adjacent gate is reduced. Thus, the contrast of an input image is improved.
Since the conductive layer having the three-layer structure included in the pin photodiode is horizontally arranged in the semiconductor layer, the conductive layer can be formed on the substrate in which the semiconductor layer is deposited on the insulating layer. An exemplary substrate that may be used is an SOI substrate in which a silicon layer is deposited on an insulating layer.
In the semiconductor device of the present invention, the n region of the pin photodiode and a source of the MOS transistor may be the same.
Since the n region of the pin photodiode and the source of the MOS transistor may be the same, a photocurrent generated in the pin photodiode is transferred to the MOS transistor at a high speed, and therefore, the current is efficiently output.
In another aspect of the semiconductor device of the present invention, a region of the semiconductor layer including the pin photodiode has a larger thickness than that of another region of the semiconductor layer including the MOS transistor, and therefore, the semiconductor layer has an optimum thickness for both the pin photodiode and the MOS transistor. Thus, the efficiency of photoconversion in the pin photodiode and the high-speed performance in switching in the MOS transistor are both improved.
Another aspect of the invention is a method for producing the semiconductor device including the element in which the pin photodiode generating a photocurrent in response to light intensity and the MOS transistor through which the photocurrent is output are integrated. More particularly, the method includes a step (first ion-implantation step) of implanting ions in a state in which a resist pattern is formed to cover at least an area for forming the p region and the i region of the pin photodiode and to expose another area for forming the MOS transistor. An SOI substrate including an insulating layer and a silicon layer deposited on the insulating layer is used. Another step (second ion-implantation step) of implanting ions in a state in which a gate electrode material is deposited on a gate oxidation layer at a position corresponding to an area for forming the gate of the MOS transistor, and in which a resist pattern is formed to cover an area for forming the p region and the i region of the pin photodiode and to expose an area for forming the source and the drain of the MOS transistor and the n region of the pin photodiode is then performed. Finally, a step (third ion-implantation step) of implanting ions in the state in which a resist pattern is formed to cover an area for forming the n region and the i region of the pin photodiode and an area for forming the MOS transistor and to expose an area for forming the p region of the pin photodiode is performed.
Since the production method of the semiconductor device has the first ion-implantation step, the second ion-implantation step, and the third ion-implantation step, the lateral pin photodiode in which the conductive layer is horizontally arranged in the semiconductor layer is provided. Thus, the pin photodiode can be formed in a substrate in which a semiconductor layer is deposited on an insulating layer.
An electronic device of the present invention has the semiconductor devices arranged in a matrix pattern. Such a structure has microelements integrated on a plane and is suitable for detecting a two-dimensional image.